Coil products are used to coat metallic substrates. The coating protects the substrate from outdoor or indoor elements and degradation (e.g., corrosion and UV degradation) as well as providing a smooth, even and appealing appearance. Some coil products are employed to make “coil coated” sheet stock. Coil coated sheet stock typically includes a roll of metallic substrate that is unwound, coated and rerolled for storage prior to fabrication. Coil products applied to such metallic substrates desirably will withstand the fabrication conditions to which the coil coated sheet stock may subsequently be subjected while meanwhile protecting the metallic substrate. The coil product accordingly should meet unique requirements for the intended use. These requirements typically include durability, hardness, flexibility, impact resistance, and the like. Unfortunately, it is especially difficult to formulate coil product coating compositions so that they will provide both high hardness and high flexibility. Normally an increase in coating hardness will require a sacrifice in coating flexibility, and an increase in coating flexibility will require a sacrifice in coating hardness. The curing or hardening conditions employed when making coil coated sheet stock also make it difficult to attain coatings with high pencil hardness values. Commercial coil coating lines usually employ a heating cycle lasting 30 seconds or less. Longer heating cycle times might in some instances provide an improvement in pencil hardness, but owing to line speed constraints and the installed equipment base it is undesirable to extend the heating cycle past 30 seconds. It can also be difficult to attain high pencil hardness values on some substrates (e.g., hot-dipped galvanized steel) or using some pigmented coatings (e.g., high gloss black coatings). Thus it has been difficult to use existing line equipment and existing formulations to fabricate a range of coil coated sheet stock whose coatings have a 0T T-bend flexibility rating using the test described in ASTM D4145-83 and a 2H or higher pencil hardness rating using the test described in ASTM D 3363-00.
From the foregoing, it will be appreciated that what is needed in the art are coil coating compositions (preferably low cost coating compositions) that provide a desirable combination of flexibility and hardness when applied to a range of substrates at commercially acceptable line speeds. Such coating compositions, articles made using these coating compositions, and methods for preparing the coating compositions and articles are disclosed and claimed herein.